1. Field of the Invention
The present invention relates to a library apparatus of a composite type magnetic tape apparatus or the like and in particular, to an improvement of a data storage medium transportation unit for selecting a data storage medium from a plurality of data storage media stored in a data storage medium container and carrying the selected data storage medium to a read/write block or returning a data storage medium from the read/write block to the data storage medium container.
2. Description of the Related Arts
There is a known configuration of the data storage medium transportation unit for holding a data storage medium between the data storage medium container and the rear/write block. For example, a data storage medium is guided by a guide rail and transported by a timing belt and a screw type feed mechanism.
FIG. 7 is a conceptual representation of such a configuration. This is an example of composite type magnetic tape apparatus in which a magnetic tape cartridge is used as the data storage medium.
The composite type magnetic tape apparatus 100 shown in FIG. 7 includes a data storage medium container 102 for storing a plurality of magnetic tape cartridges 101, a read/write block 103 for reading and writing a data from/to the magnetic tape cartridge 101, and a data storage medium transportation unit 119.
The data storage medium transportation unit 119 includes: a data storage medium holding block 104 for which reciprocally moves with a magnetic tape cartridge 101 between the data storage medium container 102 and the read/write block 103; a power transmission mechanism 105 for vertically driving the data storage medium holding block 104; and a motor 106.
The power transmission mechanism 105 includes: a guide rod 107 for vertically guiding the data storage medium holding block 104; a driven pulley 108 rotatably attached to the top of the guide rod 107; a drive pulley 109 fixed to a shaft of the motor 106, and a timing belt 110 extending between the pulleys 108 and 109 so as to surround the pulleys 108 and 109. A portion of the timing belt 110 is fixed to the data storage medium holding block 104.
Accordingly, when this motor 106 is driven, the timing belt 110 is rotated and the data storage medium holding block 104 fixed to this timing belt 110 is raised or lowered along the guide rod 107 according to the rotation direction of the motor 106, so that the data storage medium holding block 104 moves between the data storage medium container 102 and the read/write block 103.
The data storage medium holding block 104 has a pickup mechanism (not depicted) for taking out a magnetic tape cartridge 101 from the data storage medium container 102 and the read/write block 103 or remounting the magnetic tape cartridge 101, so that the magnetic tape cartridge 101 is taken out or remounted between the data storage medium container 102 or the read/write block 103 and the data storage medium holding block 104.
The data storage medium container 102 has a plurality of layered cells 111 layered in a vertical direction. In order to pass the magnetic tape cartridge 101 horizontally between a cell and the data storage medium holding block 104, the data storage medium holding block 104 should be accurately positioned to match the height of each of the cells 111.
For this, in the conventional composite type magnetic tape apparatus 100, the motor 106 serving as a drive source of the data storage medium holding block 104 has been constituted by an expensive servo motor, and a complicated control unit has been used for performing a feed back control of respective loops concerning the position and the speed.
FIG. 8 shows a concept of a general servo control. A reference symbol 112 represents a rotation-shift instruction. A microprocessor in a control unit performs pulse assignment according to a predetermined speed pattern 113 and outputs a rotation-shift instruction, i.e., a substantial rotation speed instruction for each pulse assignment cycle. Moreover, each time the microprocessor outputs the rotation-shift instruction, a value of the current rotation-shift instruction is deleted from a target value of the rotation shift amount stored in an assignment amount storage register, so as to determine a final rotation shift amount. That is, the pulse assignment processing is complete when the value of the assignment amount storage register has become zero.
The rotation-shift instruction 112 which is output from the control unit is added, for each processing cycle, to an accumulation counter 114, and a return pulse from a pulse encoder 115 of the motor 106, i.e., a feed back value of an actual rotation-shift amount of the motor 106 is deleted from the accumulation counter 114, so that a current value of the accumulation counter 114 is fed as a rotation speed instruction according to a rotation-shift deviation to an D/A converter 116. Accordingly, the motor 106 delays to follow the rotation-shift instruction 112 and the rotation-shift position deviation increases, which in turn increases the current value of the accumulation counter 114 and the value of the speed instruction. Moreover, when the rotation-shift deviation has become zero, the value the speed instruction also becomes zero, and the motor 106 retains its rotation position.
Moreover, the rotation speed instruction which is output from the D/A converter 116 is deleted by an output value of a tachogenerator 117 of the motor 106, i.e., the actual rotation speed of the motor 106, and the resultant value is fed as a torque instruction according to the rotation speed deviation, to a servo control circuit 118. Accordingly, if the motor 106 delays to follow the rotation speed instruction to increase the rotation speed deviation, the torque instruction fed to the servo control circuit 118 is also increased. Moreover, when the rotation speed deviation has become zero, the torque instruction also becomes zero, the motor 106 retains its rotation position.
The servo control circuit 118 fed with the torque instruction controls the motor 106 by power amplitude processing or the like, and vertically drives the data storage medium holding block 104 as a mechanical load via the power transmission mechanism 105.
Such a servo control enables to obtain a stable drive speed of the data storage medium holding block 104 with a high positioning accuracy. However, such a servo control requires peripheral apparatuses including the accumulation counter 114, the D/A converter 116, the servo control circuit 118, and the tachogenerator 117. That is, the production cost is increased. Moreover, in order to perform pulse assignment, the processing of the microprocessor should be performed as multi task, which increases the load of the microprocessor itself.
In order to eliminate these defects, the applicant of the present invention has suggested a data carrier loader as Japanese Patent Publication 10-366906, in which a protrusion of a data storage medium holding block is engaged with a rotary shaft having a helical groove on its circumferential portion, so that the data storage medium holding block is fed in the shaft axis direction.
The rotary shaft of this data carrier loader has a lead (distance advancing in the axis direction) zero portion as a flat portion for positioning, i.e., an interval where the position of the data storage medium holding block is not changed even if the rotary shaft is rotated, so that the positioning of the data storage medium holding block can be accurately performed even if the rotation position of the rotary shaft is not accurate. Thus, control is simplified and the positioning accuracy is increased.
The data carrier loader of Japanese Patent Publication 10-366906 can obtain a final positioning of a data storage medium holding block with a high accuracy even with rough control, and there is no need of measuring the rotation position of the rotary shaft with a high accuracy. Accordingly, the data carrier loader has, as position detection means, only a detector for detecting a turn of the rotary shaft.
Accordingly, this data carrier loader has inconvenience in detecting a shift speed and shift position of the data storage medium holding block, and in detecting abnormal operation according to the shift speed and shift position, such as an overload due to a drive system failure.
It is therefore an object of the present invention to provide a data storage medium transportation unit not requiring a complicated servo control, obtainable at a reasonable cost, and capable of detecting a shift speed and shift position of the data storage medium holding block.
The data storage medium transportation unit according to the present invention comprises:
a data storage medium holding block which holds a data storage medium and reciprocally moves between a data storage medium container and a read/write block; a motor which is a non-servo motor for driving the data storage medium holding block; a power transmission mechanism arranged between the data storage medium holding block and the motor for converting a rotary power of the motor into a drive force of the data storage medium holding block in its travelling direction; a disc-shaped rotation position detector provided in a rotary portion of the power transmission mechanism and having a plurality of identification areas arranged at an identical interval in a circumferential direction; an optical sensor provided on a non-movable portion of the data storage medium transportation unit and arranged so as to detect the identification areas of the rotation position detector; a speed control block for PWM (pulse width modulation) control of the non-servo motor, said speed control block including a counter for counting the number of identification areas detected by the optical sensor within a predetermined period of time, and a feed speed calculator for calculating a feed speed of the data storage medium holding block according to a value obtained by the counter.
Since the feed speed of the data storage medium holding block is controlled by the PWM control for a non-servo motor, there is no need of using an expensive servo motor and the production cost can be reduced.
Moreover, the rotation portion of the power transmission mechanism includes the disc-shaped rotation position detector having a plurality of identification areas which are detected by the optical sensor. The number of the identification areas detected by the optical sensor within a predetermined period of time is counted by the counter and the counted number is used by the feed speed calculator to calculate a feed speed of the data storage medium holding block. Thus, the feed speed and the feed position can be detected according to the resolution of the identification areas without applying a complicated servo control associated with feedback of the speed and the position.
Moreover, the feed speed calculated by the feed speed calculator is compared to a predetermined reference speed range. If the feed speed calculated by the feed speed calculator is out of the predetermined reference speed range, a speed error is detected by speed error detection means. Thus, it is possible to automatically detect a speed error of the data storage medium holding block.
Furthermore, the feed speed detection means is constituted so as to repeatedly calculate the feed speed of the data storage medium holding block with a cycle of the aforementioned predetermined period of time, enabling to monitor the feed speed all the time during the operation of the apparatus.
Moreover, a difference between the feed speed calculated by the feed speed calculator and a predetermined target speed is obtained and according to this difference, the duty ratio in the PWM (pulse width modulation) control is adjusted by the speed adjuster. This enables to obtain a feedback control of the feed speed substantially equivalent to a servo motor.
The identification areas of the rotation position detector may be defined by slits extending in the radial directions of the disc. The optical sensor may consist of a light emitting block and a light receiving block which are arranged so as to sandwich the rotation position detector.
Furthermore, the power transmission mechanism includes a guide member for guiding the feed direction of the data storage medium holding block, a rotary shaft having a helical groove on the outer circumference and arranged along the guide direction of the guide member, and a protrusion provided on the data storage medium holding block so as to be engaged with the groove of the rotary shaft, wherein helical groove of the rotary shaft has lead-zero flat portions for positioning. Accordingly, even by driving the motor with a rough positioning accuracy, it is possible to correctly position the data storage medium holding block at a target position.